There is nothing to tell about this military man; nevertheless, the picture has always been popular. What partly explains its charm is the contrast of the polished bib of the cuirass, the helmet of the gorgeous work and the darkly melancholic facial expression.
Such a contrast is usual for Rembrandt’s self portraits; perhaps because they began to believe that the artist’s brother is depicted here. In fact, many authorities refused to recognize the authorship of Rembrandt; their doubts were confirmed by surveys under the Rembrandt Research Program, which was funded by the Government of the Netherlands.
The “Old Man in the Helmet” is only one of the “victims” of the Program, who attributed many works to the students and followers of Rembrandt.
Related Paintings 
Polish Horseman by Rembrandt Harmens Van Rhine 
Scholarly Dispute by Rembrandt Harmens Van Rhine 
Girl by the Window by Rembrandt Harmens Van Rhine 
Shuttle of Christ in a Storm by Rembrandt Harmens Van Rhine 
Susanna and the Elders by Rembrandt Harmens Van Rhine 
Aristotle with a bust of Homer by Rembrandt Harmens Van Rhine 
Hendrickje entering the river by Rembrandt Harmens Van Rhine 
Self Portrait by Rembrandt Harmens Van Rhine
Polish Horseman by Rembrandt Harmens Van Rhine Scholarly Dispute by Rembrandt Harmens Van Rhine Girl by the Window by Rembrandt Harmens Van Rhine Shuttle of Christ in a Storm by Rembrandt Harmens Van Rhine Susanna and the Elders by Rembrandt Harmens Van Rhine Aristotle with a bust of Homer by Rembrandt Harmens Van Rhine Hendrickje entering the river by Rembrandt Harmens Van Rhine Self Portrait by Rembrandt Harmens Van Rhine